Twist-wrap film and use thereof as packaging film

ABSTRACT

The invention relates to a twist-wrap film ( 1, 2, 3 ) which is produced by coextrusion of a plurality of plastic layers. The inventive film is characterized in that at least a) one or more plastic layer(s) ( 4, 4 ′) consist of one or more semicrystalline polyolefin(s) having a uniform structure and b) at least one additional layer from an amorphous cycloolefin copolymer ( 5 ) having a uniform structure, the layers a) and b) being in direct contact. The selection of an amorphous cycloolefin copolymer having a uniform structure in at least one layer of the inventive twist-wrap film combined with a semicrystalline polyolefin having a uniform structure allows to provide a twist-wrap film that can be easily produced and that has the rigidity required for twist-wrap packagings and a satisfactory deadfold behavior, i.e., recovery behavior.

CLAIM FOR PRIORITY

This application is a continuation application of U.S. patentapplication Ser. No. 11/667,830, of the same title, having a §371 dateof May 16, 2007, which was a National Phase Patent Application based onInternational Patent Application No. PCT/EP2005/012370, filed Nov. 18,2005 (International Patent Publication No. WO 2006/058621 A1, publishedJun. 8, 2006) which, in turn, was based upon priority Austrian PatentApplication Serial No. A 2001/2004, filed Nov. 29, 2004. The prioritiesof the foregoing applications are hereby claimed and their disclosuresincorporated herein by reference.

TECHNICAL FIELD

The invention relates to a twist-wrap film that can be produced byco-extrusion of several plastic layers as well as use thereof aspackaging film.

BACKGROUND

For packaging sweets, such as candy, but also confectionery, it is knownto use so-called twist-wrap films, whereby these films are to have agood dead fold, i.e., low shape recovery, good rigidity as well astransparency. These twist-wrap films are used for twist-wrap packagings(twist packagings), whereby the packing process is carried out so thatthe twist-wrap film is wrapped around the material to be packaged, thelatter is laterally cut to length in sleeve form, and then the side endsare rotated so that the contents are protected from contaminants.

A packaging film that is suitable for the twist-wrapping consists of,for example, cellophane. The latter is characterized by transparency aswell as high rigidity. Its production, however, is often labor-intensiveand complicated.

Alternatives in this respect were found in the provision ofpolypropylene films; however, the latter have an unsatisfactory deadfold. This means that the packaging ends, i.e., the twisted ends, tendto fold back into their original form.

A switch was subsequently made to find suitable additives that improvethe shape recovery of the twist-wrap packaging. In this case, theproperties of so-called cycloolefin copolymers (COC) were used that areproduced, for example, by polymerization of ethylene with norborane withthe aid of metallic catalysts. Owing to the molecular structure thereof,cycloolefin copolymers are more rigid than low density polyethylene(LDPE) that is known in the art. By use of these cycloolefin copolymersin the form of polymer blends, the rigidity of the originally proposedtwist packaging materials based on polyethylene or polypropylene couldtherefore be increased. In this connection, sets of solutions aredisclosed in EP-A-920 989, DE-A1-195 36 043 as well as in JP-A-11077924.Another possibility of increasing the rigidity of the materials fortwist packagings was used according to JP-A-10166529 to the effect thatan adhesive layer is provided between a polypropylene film and a filmthat consists of cycloolefin copolymers. Although the rigidity desiredfor twist-packaging materials could obviously be increased by provisionof COC blends or by adhesives, these measures, on the one hand, arerelatively complex by the precise indication of the mixing ratios in thepolymer blends and, on the other hand, by use of an additionalintermediate layer in the form of an adhesive in the production oftwist-wrap films (twist-packaging materials).

Here, the invention is intended to correct this.

SUMMARY OF INVENTION

According to the invention, a twist-wrap film of the initially-mentionedtype is proposed, which is characterized in that a) one or more plasticlayer(s) of partially crystalline polyolefin(s) that is/are uniform inits (their) structure, and b) at least one additional plastic layer,uniform in its structure, consists of amorphous cycloolefin copolymer,whereby the plastic layers a) and b) are in direct contact with oneanother.

Additional advantageous configurations of the twist-wrap film accordingto the invention are disclosed according to subclaims.

In addition, the invention relates to the use of a multilayer plasticfilm, produced by co-extrusion, that consists of a) one or more plasticlayer(s) of partially crystalline polyolefin(s) that is (are) uniform inits (their) structure, and b) at least one plastic layer, uniform in itsstructure, of amorphous cycloolefin copolymer, whereby the plasticlayers a) and b) are in direct contact with one another, as packagingfilm for twist packagings.

Other configurations of the use according to the invention are disclosedaccording to subclaims.

BRIEF DESCRIPTION OF DRAWINGS

The invention is explained in more detail below based on FIGS. 1 to 3 aswell as based on embodiments. In this case, FIG. 1 shows a possibleembodiment of the twist-wrap film according to the invention based on athree-layer structure 1, while FIG. 2 shows a twist-wrap film accordingto the invention that is based on a five-layer structure 2. Anotherpossible embodiment of the twist-wrap film according to the invention isshown in FIG. 3, and here also a five-layer structure 3 is present, butwith an arrangement of the layers to one another that is different toFIG. 2.

The twist-wrap film according to the invention, as it is shown, forexample, according to FIGS. 1 to 3, can now be produced as follows:

DETAILED DESCRIPTION EXAMPLE 1

In a blown-film or cast-film system, the twist-wrap film 1, as shown inFIG. 1, is produced so that by co-extrusion on an inside layer 4 thatconsists of polyolefin, amorphous layers 5 that consist of cycloolefincopolymers are applied on both sides. In this case, the processparameters are set such that in the three-layer structure that isformed, the cycloolefin copolymer remains in an amorphous state, and theused polyolefin remains in a partially crystalline state.

By setting the machine parameters in the co-extrusion system, additionalpolyolefin layers 6 can be applied on both sides to the three-layerstructure according to FIG. 1, so that the twist-wrap film 2, as shownin FIG. 2, is produced in the form of a five-layer structure.

As polyolefin, polypropylene (PP) as well as polyethylene (PE) are used.By further selection of monomers in the molecule chain, for example inthe form of homo-PP, random-PP as well as LLDPE, additional properties,such as rigidity and dead-fold properties, can be set.

EXAMPLE 2

According to the technology described in Example 1, additionalpolyolefin layers 7 are applied to a core layer 8 that consists ofpolyolefin. In this case, the core layer 8 that is in the centerconsists of homo-PP and the bilaterally adjoining LLDPE layers 7. Onthis three-layer structure 4′ that consists of different polyolefins,the layers 5 that consist of amorphous cycloolefin copolymers are thenapplied on both sides.

In summary, it can be said that by selection of an amorphous cycloolefincopolymer that is uniform in its structure in at least one layer of thetwist-wrap film according to the invention in combination with apartially crystalline polyolefin that is uniform in its structure, onthe one hand, the rigidity that is necessary for the twist-wrappackagings and, on the other hand, a satisfactory dead fold, i.e., shaperecovery, can be produced, whereby the twist-wrap film can be obtainedat the same time in an easily producible way.

1. Twist-wrap film (1, 2, 3), which can be produced by co-extrusion ofseveral plastic layers, characterized in that at least a) one or moreplastic layer(s) (4, 4′) of partially crystalline polyolefin(s) that is(are) uniform in its (their) structure, and b) at least one additionalplastic layer, uniform in its structure, consists of amorphouscycloolefin copolymer (5), whereby the plastic layers a) and b) are indirect contact with one another.
 2. Twist-wrap film according to claim1, wherein the inner layer (4) consists of polyolefin that is uniform inits structure, which has two outer layers (5), in each case directlyadjacent on two sides, of cycloolefin copolymer that is uniform in itsstructure.
 3. Twist-wrap film according to claim 2, wherein at least oneadditional layer (6) of partially crystalline polyolefin, uniform in itsstructure, in each case directly adjoins the outer layers (5). 4.Twist-wrap film according to claim 1, wherein an inner layer (8) ofpartially crystalline polyolefin, bilaterally uniform in its structurein each case, shows another layer (7), directly adjoining, of apolyolefin that is different in its structure, whereby directlyadjoining layers (5) of amorphous cycloolefin copolymer that isbilaterally uniform in its structure in each case adjoin thisthree-layer structure (4′).
 5. Twist-wrap film according to claim 1,wherein the layers (4, 4′) consist of polyolefin or polyethylene,preferably in the form of homo-PP, random-PP or LLDPE.
 6. Twist-wrapfilm according to claim 1, wherein the latter in addition has a coverlayer, preferably in the form of an imprint and/or a metal coating, onat least one of the outside layers.
 7. Method of packaging a materialwhich comprises: providing a multilayer plastic film, produced byco-extrusion, which consists of a) one or more plastic layer(s) (4, 4′)of partially crystalline polyolefin(s), uniform in its (their)structure), and b) at least one plastic layer (5), uniform in itsstructure, of amorphous cycloolefin copolymer, whereby the plasticlayers a) and b) are in direct contact with one another, as packagingfilm for twist-wrap packagings; and wrapping the multilayer plastic filmaround the material.
 8. Method according to claim 7, provided that theplastic film consists of an inner layer (4) of polyolefin that isbilaterally uniform in its structure in each case, which has two outerlayers (5)—directly adjoining on both sides in each case—of cycloolefincopolymer that is uniform in its structure.
 9. Method according to claim8, provided that at least one additional layer (6) of a partiallycrystalline polyolefin that is uniform in its structure in each casedirectly adjoins the outer layers (5).
 10. Method according to claim 7,provided that the plastic film has an inner layer (8) of partiallycrystalline polyolefin that is uniform in its structure, which,bilaterally adjoining in its structure, has different polyolefin layers(7) in this respect and provided that amorphous cycloolefin copolymerlayers (5), which are bilaterally uniform in their structure in eachcase, directly adjoin this three-layer structure (4′).
 11. Methodaccording to claim 7, provided that as polyolefins, polypropylene, orpolyethylene are used, preferably in the form of homo-PP, random-PP orLLDPE.
 12. Method according to claim 7, provided that the plastic filmin addition has at least one cover layer, preferably in the form of animprint and/or a metal coating.